Precautions are necessary when using hydrox, since mixtures containing more than 4% oxygen in hydrogen are explosive if ignited. Hydrogen is the lightest gas (one quarter theatomic mass ofhelium or one half themolecular mass of helium) but still has a slightnarcotic potential and may causehydrogen narcosis.[4][5] Also like nitrogen, it appears to mitigate the symptoms ofhigh-pressure nervous syndrome on deep bounce dives, but reduces the density of the gas, unlike nitrogen.[6]
Although the first reported use of hydrogen seems to beAntoine Lavoisier (1743–1794) experimenting onguinea pigs, the actual first uses of this gas in diving are usually attributed to trials by the Swedish engineerArne Zetterström in 1945.[5]
Zetterström showed that hydrogen was perfectly usable to great depths. In August 1945, following a fault in using the surface equipment, he died during a demonstration dive. The study of hydrogen was not resumed until several years later by theUnited States Navy and by theCompagnie maritime d'expertises (Comex), initially during their Hydra I and Hydra II experiments, in 1968 and 1969.[7] Comex subsequently developed procedures allowing dives between 500 and 700 m (1,640 and 2,297 ft) in depth, while breathing gas mixtures based on hydrogen, called hydrox (hydrogen-oxygen) orhydreliox (hydrogen-helium-oxygen).[8]
In July 2012, after about a year of preparation and planning, members of the Swedish Historical Diving Society and theRoyal Institute of Technology Diving Club, performed a series of hydrox dives in Arne Zetterström's memory. These were performed using the same breathing mixture of 96% hydrogen and 4% oxygen as was developed and tested by Zetterström in the 1940s. The dives were made to a depth of 40 metres (131 ft), just deep enough to be able to use the oxygen-lean gas mixture. Project Leader Ola Lindh commented that in order to repeat Zetterström's record, the team would need to dive to 160 metres (525 ft), and even today a dive to that depth requires planning and equipment beyond the capabilities of most divers.[9]
A 230 m hydrox dive in thePearse Resurgence in New Zealand was made on 14 February 2023 byRichard Harris, using a Megalodon rebreather.[2] This dive is estimated to be the 54th reported experimental hydrogen dive conducted in the last 80 years by military, commercial and technical divers, and the first reported hydrogen dive using a rebreather. Two Megalodon rebreathers connected at the bailout valve were used for the dive, one withtrimix diluent (O2, N2, He), the other withhydreliox (O2, H2, He). It was also the first hydrogen diluentdive in a cave.[6]
Hydrox may be used for combatinghigh-pressure nervous syndrome, commonly occurring during very deep bounce dives,[10] and as a low-density breathing gas to minimise the work of breathing at extreme depths.[11]
The COMEX experimental series culminated in a simulated dive to 701 metres (2,300 ft), by Théo Mavrostomos on 20 November 1990 atToulon, during the COMEX Hydra Xdecompression chamber experiments. This dive made him "the deepest diver in the world".[12]
^Fife, William Paul (1979). The use of Non-Explosive mixtures of hydrogen and oxygen for diving (Report). Vol. TAMU-SG-79-201. Texas A&M University Sea Grant.
^abBrauer RW (ed). (1985). "Hydrogen as a Diving Gas".33rd Undersea and Hyperbaric Medical Society Workshop. (UHMS Publication Number 69(WS–HYD)3–1–87).Undersea and Hyperbaric Medical Society: 336 pages.
^abcOrnhagen H (1984). "Hydrogen-Oxygen (Hydrox) breathing at 1.3 MPa".National Defence Research Institute. FOA Rapport C58015-H1.ISSN0347-7665.
^abcMenduno, Michael (1 March 2023)."Hydrogen, At Last?".InDepth. GUE. Retrieved8 October 2023.
^Rostain, J. C.; M. C. Gardette-Chauffour; C. Lemaire; R. Naquet. (1988). "Effects of a H2-He-O2 mixture on the HPNS up to 450 msw".Undersea Biomed. Res.15 (4):257–70.ISSN0093-5387.OCLC2068005.PMID3212843.
^Hunger Jr, W. L.; P. B. Bennett. (1974). "The causes, mechanisms and prevention of the high pressure nervous syndrome".Undersea Biomed. Res.1 (1):1–28.ISSN0093-5387.OCLC2068005.PMID4619860.
^abFahlman, A (2000). "On the Physiology of Hydrogen Diving and Its Implication for Hydrogen Biochemical Decompression".PhD Thesis. Carleton University, Ottawa, ON, Canada.
^Lafay V, Barthelemy P, Comet B, Frances Y, Jammes Y (March 1995). "ECG changes during the experimental human dive HYDRA 10 (71 atm/7,200 kPa)".Undersea Hyperb Med.22 (1):51–60.PMID7742710.
^Ball R (2001). "Biochemical decompression of hydrogen by naturally occurring bacterial flora in pigs: what are the implications for human hydrogen diving?".Undersea Hyperb Med.28 (2):55–6.PMID11908695.
^Kayar SR, Fahlman A (2001). "Decompression sickness risk reduced by native intestinal flora in pigs after H2 dives".Undersea Hyperb Med.28 (2):89–97.PMID11908700.
